Rational design and synthesis of AIE active cationic Ir(III) complexes featuring iminopyridine ligand with dibenzosuberane core

Abstract

Novel cationic iridium(III) complexes (Ir1–Ir4) composed of iminopyridine ligands with dibenzosuberane core were synthesized. All the designed complexes Ir1–Ir4 were fully characterized through FT-IR, elemental analysis, 1H, 13C, 19F, and 31P NMR. Molecular structures of Ir1 and Ir2 are unambiguously determined by single-crystal XRD studies and thus confirm the distorted-octahedral geometry around the Ir(III) centers. Photophysical properties such as absorption, emission, and photoluminescence quantum yields (PLQYs) of Ir1–Ir4 can be accessibly finely-tuned by varying the substituents of ancillary ligands (N^N). Cyclic voltammetry (CV), and thermogravimetric analysis (TGA) were then performed to investigate the electrochemical and thermal properties of Ir1–Ir4. Solution-state emission spectra of the complexes Ir1–Ir4 showed blue-shifted emission in the range of 433 – 436 nm (PLQYs = 0.19 – 0.62 %) whereas the same complexes displayed red-shifted emission (λ max 626 – 638 nm, PLQYs = 0.31 – 0.65 %) of their solid-state emission spectra. Aggregation-induced emission (AIE) properties of Ir1–Ir4 were analyzed with dichloromethane and hexane solvent mixture. Upon aggregation (99 % of hexane), the emission intensities of Ir1–Ir4 were constantly increased with the increase of hexane concentration. Similarly, the PLQYs and lifetimes of aggregated species of Ir1–Ir4 (PLQYs = 18 – 28 % and τ = 78.8 – 101.3 ns) were excellently improved in contrast to those in pure dichloromethane solutions. Interestingly, the scanning electron microscope (SEM) images of aggregates of Ir2 exposed the hollow polymer type of morphology and such a kind of morphology derived from Ir(III) complex is not reported.